U.S. patent number 4,694,165 [Application Number 06/782,272] was granted by the patent office on 1987-09-15 for bulk material analyzer calibration block.
This patent grant is currently assigned to Gamma-Metrics. Invention is credited to Thomas L. Atwell, Clinton L. Lingren, James F. Miller, Raymond J. Proctor.
United States Patent |
4,694,165 |
Proctor , et al. |
September 15, 1987 |
Bulk material analyzer calibration block
Abstract
A calibration block is used for calibrating a bulk material
analyzer that has an activation region in which bulk material is
received for analysis and a chute for passing the bulk material
through the activation region. The block is dimensioned to be of
almost the same cross-sectional size as the interior of the chute
and extends both above and below the activation region when
inserted in the chute. The calibration block is manufactured by (a)
providing a mixture of known materials of known proportions that do
not chemically react with each other, including a bonding agent;
(b) homogenizing the mixture to make a thick paste in which the
known materials are bound without segregation of known materials
that have different densities; (c) molding the homogeneous mixture
into the shape of a block having predetermined dimensions; and (d)
solidifying the molded mixture to provide the calibration block.
Alternative processes for manufacturing the calibration block
utilize compaction and sintering techniques instead of a bonding
agent. The measurement system of the bulk material analyzer is
calibrated in accordance with measurements made while the
calibration block is in the chute. One embodiment of the
calibration block includes a plurality of uniformly distributed
holes extending through the block for receiving insertions of a
known quantity of a unique known material.
Inventors: |
Proctor; Raymond J. (San Diego,
CA), Atwell; Thomas L. (Del Mar, CA), Lingren; Clinton
L. (San Diego, CA), Miller; James F. (Solana Beach,
CA) |
Assignee: |
Gamma-Metrics (San Diego,
CA)
|
Family
ID: |
25125539 |
Appl.
No.: |
06/782,272 |
Filed: |
September 30, 1985 |
Current U.S.
Class: |
250/252.1;
250/359.1; 250/390.04; 250/505.1 |
Current CPC
Class: |
G01D
18/00 (20130101); G01N 23/222 (20130101); G01N
2223/617 (20130101); G01N 2223/3037 (20130101); G01N
2223/0745 (20130101) |
Current International
Class: |
G01N
23/222 (20060101); G01D 18/00 (20060101); G01N
23/22 (20060101); G01D 018/00 (); G01F
023/00 () |
Field of
Search: |
;250/252.1,359.1,505.1
;378/207 ;424/4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Coal Handbook; Meyers (Ed.), Dekker, New York, 1981, pp. 19-74.
.
Stewart et al.; Bureau of Mines, Technical Progress Report 74,
1974. .
Duffey et al.; American Nuclear Society Transactions, Winter 1976,
vol. 24, pp. 117-118. .
Brown et al.; Nuclear Assay of Coal, vol. 10, EPRI Document
RP983-4, Nov. 1983..
|
Primary Examiner: Howell; Janice A.
Attorney, Agent or Firm: Callan; Edward W.
Claims
What is claimed is:
1. A calibration block for use in calibrating a bulk material
analyzer, comprising
a block of a solidified homogeneous mixture of known materials in
known proportions, wherein the materials do not react chemically
with one another.
2. A calibration block according to claim 1 for use in a bulk
material analyzer having an activation region in which bulk
material is received for analysis and means for passing the bulk
material through the activation region,
wherein the block is dimensioned to be of almost the same lateral
cross-sectional size as the bulk material passage through the
activation region.
3. A calibration block according to claim 2 that is longer than the
dimension of the activation region through which the bulk material
passes.
4. A calibration block according to claim 1, wherein the known
materials include a bonding agent that binds the other known
materials and prevents segregation of known materials that have
different densities.
5. A calibration block according to claim 4, wherein the known
materials include microspheres.
6. A calibration block according to claim 1, wherein the known
materials include microspheres.
7. A calibration block according to claim 1, wherein the known
materials include phenolic microspheres.
8. A calibration block according to claim 1 containing a plurality
of holes for receiving inserts of known materials.
9. A calibration block according to claim 8 having a known quantity
of a unique known material inserted in one or more of said holes.
Description
BACKGROUND OF THE INVENTION
The present invention generally pertains to calibration of a bulk
material analyzer and is particularly directed to the composition,
use and manufacture of a calibration block for a bulk material
analyzer.
Bulk material analyzers are used to measure the elemental content
of bulk material. Such analyzers have been developed primarily to
measure the quantitative content of materials, such as ash, in
batches of coal. The parameters of interest may be determined from
the measurement of the elemental content of the bulk materials.
In a typical prior art bulk material analyzer, the bulk material is
transported through an activation region between a radiation source
and a gamma ray detector, and the detector produces signals which
are processed to provide a measurement of the elemental content of
the bulk material. Typically the radiation source is a neutron
source. When the bulk material absorbs neutrons, secondary
emissions of gamma rays are produced from the bulk material.
Different characteristic gamma ray energy spectra are produced from
different elements in the bulk materials. Accordingly, by
processing detected signals that are indicative of the gamma ray
spectrum, a measurement is provided of the elemental content of the
bulk material. This measurement process is known in the art as
prompt gamma ray neutron activation analysis (PGNAA).
In the prior art, bulk material analyzers have been calibrated by
using samples of materials of the type that are to be analyzed.
Prior to calibration, the samples are subjected to laboratory
analysis to determine their elemental content. Typically, the
samples used in the chemical laboratory analysis are relatively
small compared to the quantity of bulk material present in the
activation region during operation of the bulk material analyzer.
For example, whereas a coal analyzer typically has several hundred
pounds of coal in its activation region during operation, a coal
analysis laboratory uses only 50 grams (0.1 pounds) or less of
finely crushed coal, from which it draws sub-samples for each of
the necessary chemical analyses. Coal is a heterogeneous material.
Hence, a major source of inaccuracy in any coal analysis is the
collection of the sample of 0.1 pounds (50 grams) that is truly
representative of several hundred pounds of bulk coal. According to
the Coal Handbook, Meyers (Ed.), Dekker, New York, 1981
uncertainties in obtaining and preparing the sample are twenty
times greater than a laboratory's analytical uncertainty.
Since the first development of large scale PGNAA coal analyzers a
quick, easy and accurate method of calibration has been a problem.
Over the past ten years published research from the Electric Power
and Research Institute (EPRI) has identified the calibration
problems and attempted to solve them by several different
methods.
One such prior art method includes the step of uniformly and
accurately "spiking" moving coal streams with elements and
compounds. This method is described by R. F. Stewart et al.; Bureau
of Mines Tech. Progress Report 74, 1984. This method requires a
mechanical means to move the coal dynamically for even mixing. Only
one element can be done at a time and once a coal has been spiked
the coal must be discarded or re-used in its contaminated form.
Segregation of the coal and spike material can give large
inaccuracies. This method is not particularly easy, quick or
accurate.
Another prior art method includes the step of mixing up a powdered
plastic, or a carbohydrate sugar, and dry chemical compounds to
simulate a coal matrix and thereby provide a standard material.
This method is described by Duffey et al.; American Nuclear Society
Transactions, Winter 1976; Vol. 24, p. 117. Using this method,
different elemental coal types can be simulated. However, it is
physically difficult to achieve controllable densities with
powders. Contamination, especially from moisture, can easily occur.
Hence, care is needed in using, handling and storing the standards.
Even the most elaborate of blending methods cannot overcome the
problems of segregation between lighter and heavier material
components. Segregation gives inaccuracy. This method is quick but
not accurate nor easy.
Still another prior art calibration method uses boxes of powdered
coal that have been heavily sampled and then analyzed by many (3-5)
laboratories and thus are assumed to be "standard materials." This
method is described by Brown, Gozani & Spencer; Nuclear Assay
of Coal, Vol. 10, EPRI Document RP, pp. 983-4, Nov. 1983. In this
method, the box is analyzed simultaneously with the "standard
material". The box thus represents a non-uniformly distributed
contaminant to the "standard material". The density and freedom
from segregation cannot be maintained upon transport and handling.
Also, it is doubtful whether the "standard materials" will remain
stable in density and moisture distribution over long periods of
time when they are not hermetically sealed. This method is quick
and easy, but its accuracy does not allow a calibration that will
test a PGNAA bulk material analyzer to its limits.
SUMMARY OF THE INVENTION
The present invention provides a calibration block for use in
calibrating a bulk material analyzer. The calibration block of the
present invention is a block of a solidified homogeneous mixture of
known materials in known proportions, wherein the materials do not
react chemically with one another. In the preferred embodiment, the
known materials are standard technical grade chemicals that have
been laboratory analyzed for all of their constituent elements.
Typically, the known materials and their proportions are selected
to provide a calibration block having a proportionate elemental
composition that is typical of the bulk material that is to be
analyzed.
A preferred embodiment of the calibration block is useful in
calibrating a bulk material analyzer that has an activation region
in which bulk material is received for analysis and a chute for
passing the bulk material through the activation region. In such
embodiment, the calibration block is dimensioned to be of almost
the same lateral cross-sectional size as the bulk material passage
through the activation region. This feature coupled with the
homogeneous character of the calibration block prevents the
calibration from being affected by any spatial dependence of the
bulk material analyzer upon the lateral distribution of the
material within the activation region.
In a separate aspect, the present invention provides a process of
manufacturing a calibration block. Such process includes the steps
of (a) providing a mixture of known materials of known proportions
that do not chemically react with each other, including a bonding
agent; (b) homogenizing the mixture to make a thick paste in which
the bonding agent binds the other known materials and prevents
segregation of known materials that have different densities; (c)
molding the homogenous mixture into the shape of a block having
predetermined dimensions; and (d) solidifying the molded mixture to
provide a solid calibration block.
The preferred bonding agent is polyester resin, which is a
relatively simple homogeneous chemical that can be well
characterized as to its proportionate elemental composition. The
density of polyester resin is approximately 1.3 to 1.4 grams/cc,
whereas coal typically has a bulk density of 0.8 to 1.0 grams/cc.
In order to reduce the density of the calibration block to be
comparable to that of the material that is to be analyzed, one of
the known materials of the mixture is chosen to be microspheres.
Microspheres are small bubbles. The use of phenolic microspheres,
which have an elemental composition of carbon, hydrogen and oxygen,
enables the calibration block to be tailored by judicious choice of
the other carbon, hydrogen and oxygen containing materials to be of
a predetermined density without severely impacting the overall
elemental composition of the calibration block. In this regard, it
is noted that the PGNAA measurement technique is insensitive to
oxygen.
In further aspects, the present invention provides alternative
processes of manufacturing a calibration block that include the
techniques of compaction and sintering. One such process includes
the steps of (a) providing a mixture of known materials of known
proportions that do not chemically react with each other; (b)
homogenizing the mixture; (c) filling a shell of predetermined
dimensions with the homogenous mixture by incrementally compacting
the homogenous mixture in the shell in layers that are of such
depth as to attain uniform compaction density throughout the shell
and as to prevent substantial segregation of known materials that
have different densities; and (d) sealing the shell to provide the
calibration block.
The other alternative process of manufacturing a calibration block,
includes the steps of (a) providing a mixture of known materials of
known proportions that do not chemically react with each other; (b)
homogenizing the mixture; (c) filling a mold of predetermined
dimensions with the homogenous mixture by incrementally compacting
the homogenous mixture in the mold in layers that are of such depth
as to attain uniform compaction density throughout the mold and as
to prevent substantial segregation of known materials that have
different densities; and (d) sintering the molded mixture to
provide the calibration block.
The calibration block of the present invention is used in a method
of calibrating a bulk material analyzer that has an activation
region in which bulk material is received for analysis and
measurement means for measuring the elemental content of the
received bulk material. Such method includes the steps of (a)
inserting within the activation region a calibration block that
includes a block of a solidified homogeneous mixture of known
materials in known proportions, wherein the materials do not react
chemically with one another; (b) taking measurements with the bulk
material analyzer while the calibration block is within the
activation region; and (c) calibrating the measurement means in
response to the measurements taken in step (b) in accordance with
the known proportions of the known materials of the calibration
block.
Such method is useful for calibrating a bulk material analyzer
having a chute for passing the bulk material through the activation
region. In accordance with such method, the calibration block that
is used is dimensioned to be of almost the same lateral
cross-sectional size as the interior of the chute.
In a preferred embodiment, the calibration block that is used is
longer than the dimension of the activation region through which
the bulk material passes in order to simulate a continuous flow of
bulk material through the activation region.
One preferred embodiment of the calibration block contains a
plurality of holes. A known quantity of a unique known material is
inserted in one or more of the holes to measure the sensitivity of
the bulk material analyzer to that unique known material, or to
measure the spatial variance of the sensitivity of the bulk
material analyzer in accordance with the measurements obtained for
the inserted unique known material.
Additional features of the present invention are discussed in
relation to the description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 combines a block diagram of the manufacturing process of the
present invention that utilizes a bonding agent with a perspective
view of one preferred embodiment of a calibration block according
to the present invention.
FIG. 2 is a greatly enlarged view of a portion of the calibration
block of FIG. 1, with a portion cut away to illustrate the uniform
distribution of the known materials therein.
FIG. 3 is a perspective view of an alternative embodiment of the
calibration block of the present invention.
FIG. 4 is a perspective view, with portions cut away, of a bulk
material analyzer in which the calibration block of the present
invention has been installed for calibration of the analyzer.
FIG. 5 is a block diagram of a manufacturing process according to
the present invention that utilizes a compaction technique.
FIG. 6 is a block diagram of the manufacturing process of the
present invention that utilizes a sintering technique.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of manufacturing a calibration block in accordance with
the present invention is described with reference to FIG. 1. The
first step (a) is to provide a mixture of known materials of known
proportions that do not chemically react with each other, including
a polyester resin. The next step (b) is to homogenize the mixture
to make a thick paste in which the resin binds the other known
materials and prevents segregation of the other known materials
that have different densities. Accordingly, the lighter materials
of the mixture are not segregated from the heavier components once
the mixture has been homogenized. The third step (c) is to mold the
homogenous mixture into the shape of a block having predetermined
dimensions. The final step (d) is to solidify the molded mixture to
provide a solid calibration block 10. The mold is then removed so
that the calibration block 10 can be used.
The known components are all standard technical grade chemicals
that have been laboratory analyzed for all of their constituent
elements. Typically, the known materials and their proportions are
selected to provide a calibration block having a proportionate
elemental composition that is typical of the bulk material that is
to be analyzed. The basic composition of the calibration block 10
can be tailored by variation of the proportions of the constituent
known materials to vary the proportions of a plurality of the
constituent elements simultaneously.
The following examples describe the composition of a calibration
block that has been manufactured for use in calibrating a bulk
material analyzer for measurements of the elemental content of
different types of western coal:
EXAMPLE 1
(Western)
TABLE 1 ______________________________________ Material Weight
Percent ______________________________________ polyester resin
68.000 methylethyl ketone peroxide (hardener) 1.360 anhydrous
magnesium sulfate 3.500 iron oxide 0.600 silicon dioxide 3.000
calcium carbonate 3.500 alumina 2.400 Sodium carbonate 0.250 Nylon
6/6 7.260 titanium dioxide 0.075 potassium chloride 0.050 boron
0.005 phenolic microspheres 10.000
______________________________________
The elemental breakdown for the calibration block of Example 1 is
as follows:
TABLE 2 ______________________________________ Element Weight
Percent ______________________________________ Hydrogen 5.761 Boron
0.005 Carbon 60.268 Nitrogen 0.941 Oxygen 27.573 Sodium 0.329
Magnesium 0.449 Aluminum 0.769 Silicon 1.399 Sulfur 0.643 Chlorine
0.029 Potassium 0.027 Calcium 1.358 Titanium 0.045 Iron 0.405
______________________________________
EXAMPLE 2
(western, 24% ash, high density)
TABLE 3 ______________________________________ Material Weight
Percent ______________________________________ polyester S40 58.000
methylethyl ketone peroxide (hardener) 1.160 dry magnesium sulfate
6.500 black iron oxide 1.800 silicon dioxide 12.500 calcium
carbonate 5.460 alumina 7.100 sodium carbonate 0.250 titanium
dioxide 0.075 potassium chloride 0.050 boron 0.0046 phenolic
microspheres 7.000 ______________________________________
The elemental breakdown for the calibration block of Example 2 is
as follows:
TABLE 4 ______________________________________ Element Weight
Percent ______________________________________ Hydrogen 4.751 Boron
0.0045 Carbon 46.844 Nitrogen 0.076 Oxygen 34.522 Sodium 0.271
Magnesium 0.831 Aluminum 2.299 Sulfur 1.193 Silicon 5.787 Chlorine
0.036 Potassium 0.027 Calcium 2.109 Titanium 0.046 Iron 1.204
______________________________________
EXAMPLE 3
(western, medium density, low hydrogen)
TABLE 5 ______________________________________ Material Weight
Percent ______________________________________ polyester S40 58.000
methylethyl ketone peroxide (hardener) 1.160 dry magnesium sulfate
3.500 black iron oxide 0.600 silicon dioxide 3.000 calcium
carbonate 3.500 alumina 2.400 sodium carbonate 0.250 titanium
dioxide 0.075 potassium chloride 0.050 boron 0.005 phenolic
microspheres 10.000 graphite 16.090 polyethylene 1.370
______________________________________
The elemental breakdown for the calibration block of Example 3 is
as follows:
TABLE 6 ______________________________________ Element Weight
Percent ______________________________________ Hydrogen 4.724 Boron
0.0045 Carbon 62.922 Nitrogen 0.443 Oxygen 25.137 Sodium 0.352
Magnesium 0.468 Aluminum 1.027 Sulfur 0.693 Silicon 2.020 Chlorine
0.034 Potassium 0.091 Calcium 1.482 Titanium 0.052 Iron 0.549
______________________________________
In these calibration blocks, the elementally simple polyester resin
is the major constituent of the homogenized mixture. The proportion
of each of the minor constituent materials of the mixture is not
more than twenty percent. Hence, any laboratory analysis
uncertainties associated with the minor constituent materials are
reduced by a factor of five or greater when applied to the
constituents of the entire calibration block.
In one preferred embodiment, as shown in FIG. 1, the calibration
block 10 is a solid block. The density of the block is determined
in accordance with the proportion of microspheres included in the
mixture. Preferably, the microspheres are small, phenolic plastic
bubbles which are 50 microns in diameter, with 1 micron thick
shells. FIG. 2 illustrates the uniform distribution of the
microspheres 12 in the solidified homogenized mixture 14 of the
calibration block 10. The calibration block 10 is of rugged
one-piece construction for ease of handling.
The calibration block 10 has a consistent concentration of
constituent materials per unit volume. The materials chosen for the
calibration block are both chemically and biologically stable for a
long term period of several years. Hence, the calibration block is
dimensionally stable.
An alternative preferred embodiment of a calibration block 20
according to the present invention is shown in FIG. 3. The
calibration block 20 includes a plurality of uniformly distributed
holes 22 that extend between the ends 24 of the calibration block.
The holes 22 are created either by drilling through the calibration
block 20 or by molding the homogeneous mixture with a mold that
defines the holes 22 in the molded calibration block 20. In other
respects the calibration block 20 is manufactured in the same
manner as the calibration block 10 described above with reference
FIGS. 1 and 2.
In an embodiment, wherein the calibration block 20 has an exterior
rectangular solid shape, as shown in FIG. 3, and is dimensioned to
be approximately 1 foot (30 cm) by 3 (91 cm) feet by 5 feet (152
cm), there are twenty-seven holes in a three-by-nine matrix, with
the centers of the holes being separated by four inches (10 cm) and
the edges of the peripheral holes being two inches (5 cm) from the
adjacent edges of the end surfaces 24 of the block 20. The holes
have a 3/4 inch (1.9 cm) diameter. Tubes 26 are provided for
insertion in the holes 22. The tubes 26 are hollow aluminum tubes
of 5/8 inch (1.6 cm) external diameter. The tubes 26 are filled
with a unique known material and inserted into the holes 22 of the
block 20.
The preferred embodiments of the calibration blocks described with
reference to FIGS. 1 and 3 are dimensioned for use in calibrating
the type of bulk material analyzer that is described in U.S. patent
application No. 639,577, filed Aug. 10, 1984 for "Self-Contained,
On-Line, Real-Time, Bulk Material Analyzer" by Thomas L. Atwell et
al., now U.S. Pat. No. 4,582,992 which is commonly assigned with
the present application, and the pertinent disclosure of which is
incorporated herein by reference thereto. Such a bulk material
analyzer is shown in FIG. 4.
The bulk material analyzer includes a portable container 30. The
container is approximately eight feet (244 cm) wide by ten feet
(305 cm) long by eight feet (244 cm) high. The dimensions stated
herein are particularly applicable to a coal analyzer and may
differ for analyzers of other types of bulk materials in accordance
with the physical characteristics of the bulk material, such as
flowability.
An open-ended vertical chute 32 extends through the container 30.
An input hopper 34 is fastened to the top of the chute 32 for
receiving bulk material that is channeled through the chute 32. The
bulk material (not shown), such as coal, is fed into the hopper 34
by an input conveyor 36 and is fed away from the bottom of the
chute 32 by an output conveyor 38.
The chute 32 is particularly dimensioned in accordance with the
flow characteristics of the bulk material; and for application to
coal thereby has an interior rectangular cross section of
approximately one foot (30 cm) by three feet (91 cm) to assure that
coal which is up to 4-inch (10 cm) top size will flow therethrough
without plugging or bridging within the chute 32. The chute 32 is
approximately eight feet (244 cm) long.
Neutron radiation sources 40 are symmetrically disposed on and
outside one of the three-foot (91 cm) long sides of chute 32. The
sources 40 are adjacent to the three-foot (91 cm) long sides of the
chute 32.
Gamma ray detectors 42 are symmetrically disposed on and outside
the other of the three-foot (91 cm) long sides of the chute
opposing the positions of the neutron sources 40 on the one side of
the chute 32.
The sources 40 and the detectors 42 are aligned in a common plane
which is approximately three feet (91 cm) above the bottom of the
chute 32. The region generally between and extending above and
below past the sources 40 and the detectors 42 is referred to
herein as the activation region. In the analyzer shown in FIG. 4,
the activation region is approximately two feet (61 cm) long in the
longitudinal dimension of the chute 32.
The detectors 42 detect gamma rays that are secondarily emitted by
materials in the activation region that are bombarded by neutron
radiation from the sources 40. The detectors 42 produce signals in
response to the detected gamma rays. These produced signals are
characteristic of the elemental content of the bulk material in the
activation region.
The sources 40 and detectors 42 are relatively disposed as
described above for causing the measurements to be independent of
the lateral distribution of the bulk material in the chute 32.
The bulk material analyzer further includes a measurement system 44
for combining and processing the signals produced by the detectors
42 to provide a measurement of the elemental content of the bulk
material that is channeled through the activation region by the
chute 32.
The calibration block 10, 20 is dimensioned to be of almost the
same lateral cross-sectional size as the interior of the chute 32,
being only slightly smaller so that it 10,20 can be inserted into
the chute 32. FIG. 4 shows a calibration block 10 (dashed lines)
inserted within the chute 32. The calibration block 10 is longer
than the activation region. In the embodiment of FIG. 4, the
calibration block is five feet (152 cm) long and extends both above
and below the two-foot (61 cm) long activation region when inserted
in the chute 32 for calibrating the bulk material analyzer. The
calibration block 10 thereby simulates the continuous flow of bulk
material through the activation region.
The following method is employed to calibrate the bulk material
analyzer of FIG. 4 with the calibration block 10. The calibration
block 10 is inserted into the chute 32, as shown in FIG. 4 and
described above. Next, measurements of elemental content are taken
by the measurement system 44 for all of the elements in the
calibration block 10 while the calibration block 10 is in the chute
32. Finally, the measurement system 44 is calibrated in response to
the measurements taken while the calibration block 10 is in the
chute 32 in accordance with the known proportions of the known
materials of the calibration block 10.
The calibration block 20 having the holes 22 extending therethrough
is used in two alternative embodiments of the method of calibrating
the bulk material analyzer of FIG. 4. In one such alternative
embodiment, each of the tubes 26 is filled with a known quantity of
a unique known material, the tubes 26 are placed in all of the
holes 22 and measurements are made with the measurement system 44.
The measurements system 44 is then calibrated in accordance with
such measurements so that the bulk material analyzer can make
accurate measurements of the elemental content of such unique known
material when it is present in the type of bulk material simulated
by the integral portion of the calibration block 20. In these
embodiments measurements are also made with empty tubes 26 inserted
in the same manner as the filled tubes in order to account for the
composition of the tubes 26.
In the other such alternative embodiment using the calibration
block 20, the bulk material analyzer is calibrated for variations
in its spatial sensitivity. In this embodiment, only one of the
tubes 26 is filled with a unique known material. This tube 26 is
inserted in only one of the holes 22 at a time, but is sequentially
inserted in each of the holes 22. While the tube 26 is in each hole
22, measurements are taken of the elemental content of the unique
known material. These measurements provide an indication of the
sensitivity of the bulk material analyzer to lateral variations of
the position of the unique known material. The sensitivity of the
bulk material analyzer to vertical variations of the position of
the unique known material is determined by inserting a small slug
in the one tube 26 and by varying the depth of insertion of the
slug into the activation region for each of the holes 22 of the
calibration block, with a measurement being taken for each depth of
insertion for each hole 22 to provide a complete three-dimensional
profile of the spatial sensitivity of the bulk material analyzer.
These measurements are then used to refine the calibration of the
measurement system.
Alternative to the use of a slug at varied depths, a tube 26 is
partially filled to a given depth with a unique known material and
such depth is varied as the measurements are taken to obtain the
three-dimensional profile.
FIG. 5 shows a process of manufacturing a calibration block
according to the present invention that utilizes a compaction
technique. The first step (m) is to provide a mixture of known
materials of known proportions that do not chemically react with
each other. The next step (n) is to homogenize the mixture. The
third step (o) is to fill a shell of predetermined dimensions with
the homogenous mixture by incrementally compacting the homogenous
mixture in the shell in layers that are of such depth as to attain
uniform compaction density throughout the shell and as to prevent
substantial segregation of known materials that have different
densities. The final step (p) is seal the shell to provide the
calibration block 50. The shell forms the outer skin of the
calibration block 50.
FIG. 6 shows a process of manufacturing a calibration block
according to the present invention that utilizes a sintering
technique. The first step (w) is to provide a mixture of known
materials of known proportions that do not chemically react with
each other. The next step (x) is to homogenize the mixture. The
third step (y) is to fill a mold of predetermined dimensions with
the homogenous mixture by incrementally compacting the homogenous
mixture in the mold in layers that are of such depth as to attain
uniform compaction density throughout the mold and as to prevent
substantial segregation of known materials that have different
densities. The final step (z) is sinter the molded mixture to
provide the calibration block 60. The mold is then removed so that
the calibration block 60 can be used.
For both of the processes of FIGS. 5 and 6, the known components
are all standard technical grade chemicals that have been
laboratory analyzed for all of their constituent elements. These
two processes provide the advantage of not having to utilize a
bonding agent, when the bonding agent includes elements that are
not desired in the calibration block.
The following example describes the composition of a calibration
block that has been manufactured according to the process of FIG. 5
for use in calibrating a bulk material analyzer for measurements of
the content of a given type of cement.
EXAMPLE 4
TABLE 7 ______________________________________ Material Weight
Percent ______________________________________ silicon dioxide
13.70 alumina 2.39 ferric oxide 2.33 calcium carbonate 75.64
magnesium carbonate 5.94 ______________________________________
For this example, the mixture was incrementally compacted in layers
that were approximately one inch (2.5 cm) deep.
The calibration blocks 50, 60 manufactured by the processes of
FIGS. 5 and 6 are used to calibrate a bulk material analyzer in the
same manner as with the calibration block 10 described
hereinabove.
For ease of handling, a plurality of identically constituted small
calibration blocks (not shown) may be used in lieu of one large
calibration block.
Also, although a rectangular shape is preferred for a calibration
block used in a chute having a rectangular horizontal
cross-section, such as in the bulk material analyzer of FIG. 1;
alternatively, a plurality of indentically constituted spherical
calibration blocks (not shown) can be used. The spherical blocks
are poured into the chute 12 up to a level above the activation
region and the calibration measurements are taken in the same
manner as with the large singular calibration block 26. Spherical
calibration blocks are preferred over the rectangular cross-section
calibration blocks when the chute of the bulk material analyzer has
a rounded horizontal cross section.
* * * * *